The present invention relates to the deposition of organic material through a mask onto a substrate in the process of making an organic light emitting diode (OLED).
In making organic light emitting devices (OLED) there are a number of steps in which organic layers are deposited on or over a substrate. It is essential that a deposition mask be aligned and properly mounted so that accurate deposition takes place in the appropriate place. The deposition mask is typically a precision mask made of a magnetic material and is thin and malleable. The deposition mask is lithographically patterned and because it is thin permits the appropriate thickness of organic material to be deposited on or over the substrate. The deposition mask has to be properly mounted and then aligned to the substrate. The following is a description of a standard technique used to mount and align the deposition mask. Prior art typically uses a frame and manually centers the deposition mask relative to the frame. Typically, tape is used to secure the frame to the deposition mask. In this process, after the tape secures one edge to the deposition mask, the deposition mask is placed in tension and secured on its opposite edge by tape. The frame with the mounted deposition mask is then positioned in vacuum chamber relative to the substrate. An alignment camera is typically used to provide a fine scale positioning of the frame so that the deposition mask is properly aligned prior to deposition. This is a highly time consuming process. The process is subject to errors because there is a subjective judgement made during the visual alignment. Another problem is that during tensioning of the deposition mask, ripples can be formed in such deposition mask.
It is an object of the present invention to provide an improved way of accurately positioning a deposition mask on the surface of a substrate minimizing visual errors and rippling caused by tensioning.
This object is achieved by an alignment device for permitting a deposition mask to be positioned relative to a substrate to facilitate deposition of organic material on to the substrate which will be part of an organic light emitting device, comprising:
(a) a base having a first set of alignment pins and a second set of alignment pins;
(b) a plate secured to the base;
(c) a frame having an opening aligned with the plate, the frame being formed with a first set of alignment pin receiving holes corresponding to the position of the first set of pins so that the frame is removably mounted to the base;
(d) the deposition mask positioned on the plate;
(e) a transparent flat plate contacting the second set of pins and the deposition mask and being sized to expose portions of the deposition mask; and
(f) means for securing the exposed portions of the deposition mask to the frame.
An advantage of the present invention is that the deposition mask can accurately be positioned in contact with the surface of the substrate preventing rippling of the deposition mask thereby providing improving the yield in making organic light emitting diodes. In one embodiment by providing magnets in the frame and magnetic material in the deposition mask, the alignment of the deposition mask on the frame can be closely spaced to the organic light emitting device.